1. Field of the Invention
The present invention relates to a method of producing a multi-apertured component having in use a fluid flow therethrough which is as close as possible to a predetermined value. The invention is applicable in particular to the production of components for a gas turbine, such as turbine blades or combustor cooling rings.
In producing components of the above-mentioned type, it is desirable that the fluid flow through the apertures be as close as possible to a predetermined desired value. Conventionally, the apertures are formed (such as by laser drilling) using specific process parameters and, after all of the apertures having been so produced, the overall fluid flow through the component is measured to check that it comes reasonably close to the desired value. Using this technique, it is possible to achieve a typical tolerance of .+-.10%.
2. The Prior Art
EP-A-0417917 discloses methods of forming multi-apertured components to much closer tolerances in which a first aperture or a first series of apertures is formed in a component and, subsequently at least one further aperture or at least one further series of apertures is formed in the component, prior to the formation of each such further aperture or series of apertures, the fluid flow through substantially all of the previously-formed apertures is measured, the measured fluid flow is compared with the predetermined value, and the size of the further aperture or further series of apertures is adjusted in accordance with the comparison.
U.K. Patent Publication No. 2239206 discloses a process for measuring the size of high-precision through-bores produced by laser radiation in workpieces during a boring process. Each bore is made by means of a plurality of successive energy pulses, the focal points of which are offset relative to one another in relation to the bore axis. The measurement variable is obtained from a fluid flowing through the through-bore and supplied to the boring point of the workpiece at a predetermined constant pressure. An enclosure for the fluid is provided by a chamber whose pressure is monitored in a bore to provide control of the laser in response to a comparator which also receives a desired value from a transmitter.
Desirably, the fluid flow is measured as a pressure differential across the apertures produced by a constant mass flow of fluid. The constant mass flow of fluid is advantageously produced using a critical flow nozzle and a pressure regulator upstream thereof.